Toothbrush

ABSTRACT

A tooth brush comprises a plurality of tufts each of which comprises a plurality of bristles embedded respectively in bored holes which are vertically and laterally formed in a head portion of the toothbrush. The tufts each comprises first and second bristles, such that in each of the tufts, the total of the first and second bristles is 50% or more, in number. The first bristles are tapered bristles having a factorial coefficient n=0.29 to 0.51 in the equation (I) r(x)=a{(L-x)/L} n . The distal ends of the second bristles are located in a lower position than the distal ends of the first bristles, vertical intervals between the bored holes are from 1.2 mm to 3.0 mm, and lateral intervals are from 0.75 mm to 1.5 mm. In formula (I), r(x): sectional radius, x: length from base of each bristle, L: length to distal end from base of each bristle, a: sectional radius in case x=O[=r(O)], n: factorial coefficient.

TECHNICAL FIELD

The present invention relates to a toothbrush, and more particularly toa toothbrush which is excellent in performance with regard to thecleansing of surfaces of teeth and gums, the areas between adjoiningteeth, and the marginal areas between the teeth and the gums. Thetoothbrush of the present invention is also excellent in performancewith regard to the massaging of gums, is comfortable in the sense offeel, and is satisfactory in providing a long service life.

BACKGROUND ART

Ordinary toothbrushes are chiefly designed for the purpose of cleansingthe surfaces of the teeth and gums, the areas between adjoining teeth(the areas between adjoining teeth are hereinafter referred to as"interproximal areas") and the marginal areas between the teeth and thegums (the marginal areas are hereinafter referred to as the "periodontalareas"), and removing dental plaque in the interproximal areas and theperiodontal areas. This performance is hereinafter referred to as"cleansing performance". Also, the brushing with a toothbrush provides amassaging effect against the gums. Massaging the gums is known to beremarkably effective in preventing periodontitis or gumboil. Thismassaging effect is also one of the objects of toothbrush devices. Inorder to improve the cleansing performance, various types oftoothbrushes have heretofore been proposed.

One such example is disclosed in Japanese Utility Model Publication No.Sho 61-10495 in which a toothbrush has tapered bristles and non-taperedbristles alternately embedded. The tapered bristles cleanse theinterproximal areas and/or the periodontal areas, while the non-taperedbristles cleanse the surfaces of the teeth and gums. However, thistoothbrush does not take into consideration a massaging effect againstthe gums. Therefore, the cleansing performance and massaging effect wereleft incompatible.

Another Japanese Utility Model Publication No. Sho 63-31640 discloses atoothbrush in which non-tapered bristles having ball-like distal ends ofdifferent height are embedded such that the distal ends are steppinglyarranged, so that the massaging effect will be enhanced. However, sincethis toothbrush has non-tapered bristles having ball-like distal ends,the distal end portions are difficult to flex. Moreover, it has room forimprovement with respect to the removal of plaque and a massagingeffect.

Another Japanese Laid-Open Utility Model Application No. Hei 5-15834discloses a toothbrush having bristles which are all tapered. Thistoothbrush is not sufficient in stiffness as a whole and its bristlestend to overly flex. Accordingly, in spite of its comfortableness insense of feel, it has deficiencies in cleansing performance andmassaging effect.

Furthermore, Japanese Laid-Open Patent Application No. Hei 7-284412 andU.S. Pat. No. 5,500,975 disclose a toothbrush in which two types ofbristle end forms, one being of a ball-like shape and the other being ofa tapered shape, are folded into two parts and embedded in bored holesrespectively. This toothbrush has, indeed, the advantages that theball-like end form of its bristles provides a good massaging effect tothe gums and a good plaque scraping-off effect, and that the tapered endform provides a good plaque-removing effect from the periodontal pocket.However, in spite of those advantages, this toothbrush has thedeficiencies that the bristles having the ball-like end form are moredifficult to be flexed than the bristles having the tapered end form,and that the first-mentioned group of bristles having the ball-like endform are degraded in sense of feel and comfortableness. Moreover, thistoothbrush is also not satisfactory with respect to long service life.

The inventors of the present invention have studied very hard in orderto overcome the above-mentioned deficiencies and finally succeeded inthe development of a toothbrush capable of overcoming thosedeficiencies. It is, therefore, an object of the invention to provide atoothbrush which is excellent in performance with respect to thecleansing of surfaces of the teeth and gums, the areas between adjoiningteeth, and the marginal areas between the teeth and the gums, andexcellent in performance with respect to the massaging of gums, iscomfortable in sense of feel, and is satisfactory in providing a longservice life.

DISCLOSURE OF INVENTION

According to a feature of the present invention, there is provided atoothbrush comprising: a plurality of tufts each of which comprises aplurality of bristles embedded respectively in bored holes which arevertically and laterally formed in a head portion of the toothbrush;wherein: each of said tufts comprises first and second bristles, and ineach of said tufts, a total of the first and second bristles is 50% ormore. The first bristles are tapered bristles having a factorialcoefficient n=0.29 to 0.51 in the following equation (1). Distal ends ofthe second bristles are located in a lower position than distal ends ofthe first bristles. Vertical intervals between each of said bored holesare from 1.2 mm to 3.0 mm, and lateral intervals between each of saidbored holes are from 0.75 mm to 1.5 mm;

    r(x)=a{(L-x)/L}.sup.n                                      (I)

where

r(x): sectional radius

x: length from base of each bristle

L: length to distal end from base of each bristle

a: sectional radius in case x=0[=r(0)]

n: factorial coefficient

According to a further feature of the present invention, the tufts eachinclude from 10% to 90% of the first bristles and from 90% to 10% of thesecond bristles.

According to a further feature of the present invention, a step dbetween the distal end of each of the first bristles and the distal endof each of the second bristles is from 0.5 mm to 4.0 mm.

According to a further feature of the present invention, an outerdiameter of the bases of each of the first bristles and each of thesecond bristles is from 0.15 mm to 0.30 mm, and an inside diameter ofeach of the bored holes is from 1.2 mm to 2.4 mm.

According to a further feature of the present invention, the secondbristles each have a ball-like portion formed on a distal end portionthereof.

According to a further feature of the present invention, the secondbristles are tapered towards the distal ends.

BRIEF DESCRIPTION OF DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings wherein:

FIG. 1 is a side view showing one embodiment of a toothbrush accordingto the present invention;

FIG. 2 is a perspective view showing a head portion in the above oneembodiment according to the present invention;

FIG. 3 is a side view showing bristles in the toothbrush according tothe present invention;

FIG. 4 is a side view showing distal end portions of the first andsecond bristles when brushing is made in the above one embodiment of thetoothbrush according to the present invention;

FIGS. 5(a)-5(e) are side views showing various shapes of the taperedsecond bristles in the toothbrush according to the present invention;

FIGS. 6(a)-6(e) are side views showing various shapes of ball-likeportions formed on the distal ends of the bristles in the toothbrushaccording to the present invention;

FIG. 7 is a perspective view showing a construction of an abrasivedevice used for manufacturing a toothbrush of the present invention;

FIG. 8 is an enlarged perspective view showing the brush portion of theabrasive device used for manufacturing a toothbrush of the presentinvention; and

FIG. 9 is a side view showing one mode for steppingly grinding atoothbrush in the abrasive device used for manufacturing the toothbrushof the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring now to the drawings, wherein like reference numerals designateidentical or corresponding parts throughout the several views, oneembodiment of a toothbrush according to the present invention will nowbe described. FIG. 1 is a side view of this embodiment, FIG. 2 is aperspective view showing a head portion in this embodiment, FIG. 3 is aside view showing bristles according to this embodiment, and FIG. 4 is aside view showing distal ends of the first and second bristles accordingto this embodiment when brushing.

As shown in FIGS. 1 and 2, the toothbrush according to the presentinvention includes a plurality of tufts 1 each including a plurality ofbristles, the tufts 1 being embedded respectively in bored holes 21, 21. . . which are vertically and laterally formed in a head portion 2. Thetoothbrush of this embodiment is not different from the relatedtoothbrushes in this respect.

As shown in FIG. 2, the toothbrush of this embodiment has the featuresthat the tufts 1 each comprise first and second bristles 11, 12, in eachtuft 1, the total of the first and second bristles 11,12 is 50% or more,in number. Each of the tufts 1 includes from 10% to 90% of the firstbristles 11, and from 90% to 10% of the second bristles 12. The firstbristles 11 are tapered bristles which have a factorial coefficientn=0.29 to 0.51 in the below-listed equation (I). The distal ends of thesecond bristles 12 are located in a lower position than the distal endsof the first bristles 11, vertical intervals P₁ between the bored holes21, 21 . . . are from 1.2 mm to 3.0 mm, and lateral intervals P₂ arefrom 0.75 mm to 1.5 mm.

    r(x)=a{(L-x)/L}.sup.n                                      (I)

In the above equation (I), "r(x)" is a function of x and represents aradius of a circular cross-section of the bristle, "x" represents alength from the base of the bristle, "L" represents a length of thebristle from its base to its distal end, "a" represents a value of"r(0)" (sectional radius in case x=0), and "n" represents a factorialcoefficient. In the case of the present invention, the factorialcoefficient "n" is a value in a range from 0.29 to 0.51.

It should be noted that although FIG. 2 shows only one each of the firstbristle 11 and the second bristle 12 for the sake of clarity of theconstruction of the head portion 2, a plurality of the first bristles 11and a plurality of the second bristles 12 are, in actual practice,embedded respectively in the bored holes 21 as shown in FIG. 1.

The toothbrush according to this embodiment will be described in moredetail. As shown in FIG. 1, the toothbrush of this embodiment includes,as in the ordinary toothbrushes, the head portion 2 with a plurality ofthe tufts 1, 1 . . . embedded therein, a handle portion 4 to be grippedin use, and a neck portion 3 interposed therebetween for connecting thehead portion 2 and the handle portion 4 together.

The bristles 11, 12 embedded in the bored holes 21, 21 . . . are made ofpolybutylene terephthalate (PBT), nylon (6-12, 6-10, 6-6),polypropylene, or the like. Each bristle is folded generally at itscenter into two parts so that one of the two parts forms the firstbristle 11 and the other part forms the second bristle 12, and isinserted and embedded in the corresponding bored hole 21 with its foldedpart supported by a flat plate 22 as shown in FIG. 2.

It should be noted that although FIG. 2 shows only one each of the firstbristle 11 and second bristle 12 for the sake of clarity of theconstruction, a plurality of such first and second bristles 11, 12 are,in actual practice, embedded respectively in the bored holes 21.

As shown in FIGS. 2 and 3, the first bristles 11 have a tapered formobtained by the aforementioned equation (I). The first bristles 11 aretapered by mechanical means such as a grinder or by chemical meansthrough chemical treatment under usual practice. In this embodiment, thefirst bristles 11 and the second bristles 12 are tapered by mechanicalmeans as later described in detail.

The first bristles 11 are preferably from 9 mm to 13 mm in height h. Ifthe height h of the first bristles 11 are less than 9 mm, the firstbristles 11 become extremely difficult to be flexed to thereby degrademassaging performance and cleansing performance. On the contrary, if theheight h of the first bristles 11 are more than 13 mm, the bristlesinterfere when brushing and the stiffness of the bristles 11 is overlydecreased to degrade massaging performance and cleansing performance.

The thickness of the non-tapered portions of the first and secondbristles 11, 12 is preferably from 0.15 mm to 0.30 mm in diameter. Ifthe thickness is less than 0.15 mm in diameter, the stiffness of thebristles 11, 12 is overly decreased to degrade massaging performance andcleansing performance, and the bristles are liable to be cut and badlyworn to sacrifice the long service life. On the contrary, if thethickness is greater than 0.30 mm in diameter, the stiffness is overlyincreased to degrade massaging performance and cleansing performance.Viewing the massaging performance and cleansing performance, it ispreferred that about from 9 to 25 pieces of the first and secondbristles 11, 12 in combination are embedded in each bored hole 21(although that is also under influence of the relation between thelargeness of each bored hole 21 and the thickness of the bristles 11,12).

The first bristles 11, as mentioned above, have a configuration asindicated by the above equation (I). In the equation (I), the closer "n"comes to 0, the more the configuration of each bristle resembles acircular column-like configuration, and the closer "n" comes to 1, themore each bristle resembles a cone-like configuration. In the case ofthis embodiment, "n" takes a value within the range of from 0.29 to 0.51and the first bristles 11 each take a streamline-like distal endconfiguration.

Since the first bristle 11 takes a tapered form as indicated by theabove equation (I) in case the factorial coefficient "n" is from 0.29 to0.51, the toothbrush according to this embodiment readily enters intothe interproximal areas and the periodontal areas, not overly hard andtherefore, is comfortable in sense of feel, has a stiffness which issuitable to massage the gums, and has a satisfactory long service life.That is, in order to satisfy all of those effects, the factorialcoefficient "n" must be within the above-mentioned range.

If the factorial coefficient "n" is less than 0.29, each of the firstbristles 11 takes a form more resembling a circular column, and thestiffness of the first bristles 11 are overly increased to provide ahard sense of feel. Moreover, it causes the second bristles 12 to besomewhat raised from the surfaces of the teeth when brushing, instead ofappropriately touching the surfaces. Accordingly, the first bristles 11are difficult to co-act with the second bristles 12, thereby degradingcleansing performance and massaging performance. On the contrary, if thefactorial coefficient "n" is more than 0.51, each first bristle 11 takesa form more resembling a circular cone and the stiffness is overlydecreased. As a consequence, the first bristle 11 is overly flexed toenter between the second bristles 12 and the teeth, and between thesecond bristles 12 and the gums when brushing. Accordingly, the firstbristles 11 are difficult to co-act with the second bristles 12, therebydegrading cleansing performance and massaging performance. It ispreferable that the factorial coefficient "n" takes a value in a rangefrom 0.33 to 0.40, because the service life is increased.

Surface roughness Ra of each first bristle 11 at an area of from 30% to80% of its overall length near its distal end is from 0.5 μm to 1.5 μm.In one example, this measurement of Ra is carried out with the use of alaser type surface configuration measuring microscope. Although FIG. 3shows one example of a bristle which is folded generally at its centerinto two parts so that one of the two parts forms the first bristle 11and the other part forms the second bristle 12, the bristles of thetoothbrush according to this embodiment are, in actual practice, groundinto a tapered form after the bristles are embedded.

Since each first bristle 11 takes a tapered form and the above-mentionedsurface roughness within the aforementioned range, its distal endportion readily enters into the interproximal areas and the periodontalareas, and it is excellent in cleansing performance. Moreover, since thedistal end is readily flexed, it is comfortable in sense of feel. Inaddition, although the distal end is readily flexed, dental plaque anddirt are efficiently scraped off with its side face. If the surfaceroughness Ra is less than 0.5 μm, the side face of the first bristle 11becomes too planar to offer the scraping off effect with its outer sideface. As a consequence, plaque removing performance is decreased. On thecontrary, if Ra is more than 1.5 μm, not only will manufacturing becomedifficult, but also the service life of the first bristle 11 isdecreased. Further, if the range of the surface roughness is less than30% of its overall length near the distal end, the range of area, whichis excellent in scraping off effect, is overly reduced and no sufficientscraping effect can be obtained. On the contrary, if the range of thesurface roughness is more than 80%, the service life is decreased and inaddition, manufacture is difficult.

On the other hand, the second bristles 12 are formed at their distalends with the ball-like portions 12a and tapered towards their distalends as shown in FIGS. 2 and 3. In order to form a ball-like portion atthe distal end of the tapered bristle, the distal end of the bristle isheated to form the ball-like portion after the bristle is preliminarilytapered, or the bristle is tapered by chemical treatment or mechanicalmeans such as a grinder after the ball-like portion is formed on acircular column like bristle. The term "ball-like portion" used hererefers to one in which the maximum lateral outer diameter of theball-like portion is larger than the outer diameter of the base portionof the ball-like portion.

The maximum lateral outer diameter of each ball-like portion 12a whichis formed at the distal end of the second bristle 12, is preferably from0.15 mm to 0.38 mm. If it is less than 0.15 mm, a sufficient massagingeffect is difficult to obtain and the effect for scraping off dirt andplaque on the surfaces of the teeth and gums is difficult to obtain. Onthe contrary, if it is more than 0.38 mm, manufacture becomes difficultand in addition, each tuft 1 of the bristles becomes difficult to flex,thus it becomes unpractical to use the toothbrush.

The ball-like portions 12a formed at the distal ends of the secondbristles 12 may be formed into various forms as shown in FIGS.6(a)-6(e). In an examples of FIGS. 6(a) through 6(c), a perfectball-like portion varies in size. In a further example of FIG. 6(d), theball-like portion 12a is vertically expanded. In a further example ofFIG. 6(e), the ball-like portion 12a is horizontally expanded. In afurther example of FIGS. 5(a)-5 (e), the tapered form of the secondbristles 12 is optional. However, it preferably takes one of the formsobtained by the aforementioned equation (I) as in the case with thefirst bristles 11. If the second bristles 12 are designed to have thetapered form obtained by the equation (I), a longer service life can beobtained.

Surface roughness Ra of each second bristle 12 at an area of from 30% to80% of its overall length near its distal end is also from 0.5 μm to 1.5μm. If the surface roughness Ra is less than 0.5 μm, the side face ofthe first bristle 11 becomes too planar to obtain a satisfactoryscraping effect by the outer side face. As a consequence, plaqueremovability is degraded. On the contrary, if Ra is more than 1.5 μm,manufacture becomes difficult and in addition, the service life of thefirst bristle 11 is decreased. Further, if the range of the area havingthe surface roughness is less than 30% of its overall length near thedistal end, the range which is good for the scraping off effect is toosmall to obtain a sufficient scraping off effect. On the contrary, if itis more than 80%, the service life is decreased and manufacture becomesdifficult.

The head portion 2 has a stepped configuration in which its centralportion 50 is recessed (FIG. 2). Two rows respectively of three piecesand four pieces of the bored holes 21, 21 . . . are formed in itsforward area 51, three rows each of five pieces of the bored holes 21,21 . . . are formed in its central area 50, and two rows respectively offive pieces and four pieces of the bored holes 21, 21 . . . are formedin its rearward area 52.

Each bored hole 21 is designed to have a diameter from 1.2 mm to 2.4 mm,though a good range of the diameter depends on the thickness andhardness of the bristles 11, 12 to be embedded. If the diameter is lessthan 1.2 mm, one such tuft 1 of the bristles is overly reduced instiffness. Therefore, massaging performance and cleansing performanceare degraded. On the contrary, if the diameter is more than 2.4 mm, onesuch tuft 1 of the bristles is overly increased in stiffness. Thereforemassaging performance and cleansing performance are degraded.

A step "D" formed on the central portion 50 of the head portion 2 isprovided so that the tufts 1, 1 . . . of the bristles embedded in thehigher stage (forward area 51 and rearward area 52) may have a greatergrade of stiffness than that of the tufts 1, 1 . . . embedded in thelower stage (central portion 50). Accordingly, cleansing performance isenhanced by the tufts 1. Since the tufts 1 of the bristles embedded inthe lower stage has a lower grade of stiffness than that of the tufts 1embedded in the higher stage, the toothbrush as a whole is not overlyincreased in stiffness and therefore, massaging performance and thesense of feel are not degraded.

The step D is preferably from 0.5 mm to 3.0 mm. If it is less than 0.5mm, no difference in grade of stiffness is created between the tufts 1embedded in the higher stage (areas 51 and 52) and the tufts 1 embeddedin the lower stage (portion 50). On the contrary, if it is more than 3.0mm, since the difference in grade of stiffness between the tufts 1embedded in the higher stage (areas 51 and 52) and the tufts 1 embeddedin the lower stage (portion 50) is overly increased, it becomesdifficult to enhance cleansing performance without degrading massagingperformance and the sense of feel.

The bored holes 21, 21 . . . are arranged preferably at verticalintervals of from (as indicated by P₁ of FIG. 2) 1.2 mm to 3.0 mm, andat lateral intervals of from (as indicated by P₂ of FIG. 2) 0.75 mm to1.5 mm. If the intervals PI and P₂ are less than 1.2 mm and 0.75 mm,respectively, the adjoining tufts 1, 1 are too near to flex and thestiffness as a whole is overly increased to thereby degrade massagingperformance and cleansing performance. On the contrary, if the intervalsP₁ and P₂ are more than 3.0 mm and 1.5 mm, respectively, the adjoiningtufts 1, 1 are so far that the tufts 1, 1 are readily flexed and as aresult, the stiffness as a whole is overly decreased to thereby degrademassaging performance and cleansing performance.

With respect to the ratio of area occupied by the bored holes 21, 21 . .. on the surface of the head portion 2, the ratio is preferably from 20%to 35%. If the ratio is less than 20%, the tufts 1, 1 are too rare onthe top of the head portion 2 and the stiffness as a whole is overlydecreased to degrade massaging performance and cleansing performance. Onthe contrary, if the ratio is more than 35%, the tufts 1, 1 . . . aretoo dense on the top of the head portion 2 and the stiffness as a wholeis overly increased to degrade massaging performance and cleansingperformance.

Though the length of the first bristles 11 at the forward area 51 andthe rearward area 52 of the head portion 2 is different from that of thefirst bristles 11 at the central portion 50 of the head portion 2, thedistal ends of all the first bristles 11 are generally on the same levelof height. Similarly, though the length of the second bristles 12 at theforward area 51 and the rearward area 52 of the head portion 2 isdifferent from that of the second bristles 12 at the central portion 50of the head portion 2, the distal ends of all the second bristles 12 aregenerally on the same level of height.

As previously mentioned, a step "d" is formed between the distal end ofeach first bristle 11 and the distal end of each second bristle 12. Thestep "d" is set to from 0.5 mm to 4.00 mm. The step "d" is provided tomake it easy for the distal ends of the first bristles 11 to flex asshown in FIG. 4 during brushing. Also, owing to the provision of thestep "d", a comfortable sense of feel is obtainable and the distal endsof the first bristles 11 can easily enter the interproximal areas andthe periodontal areas in order to scrape off dirt and dental plaquetherefrom. Further, the ball-like portions 12a of the second bristles 12provide a favorable massaging effect to the gums, and dirt and dentalplaque accumulated on the surfaces of the teeth and gums can be scrapedoff by the ball-like portions 12a. Furthermore, since the secondbristles 12 are tapered, only the distal end portions of the secondbristles 12 can easily be flexed without degrading cleansing performanceand massaging performance, thereby providing a more comfortable sense offeel and a long service life of the bristles.

If the step "d" is less than 0.5 mm, the distal ends of the firstbristles 11 are not flexed but merely allowed to contact the surfaces ofthe teeth and gums simultaneous with the ball-like portions 12a of thesecond bristles 12. Accordingly, the sense of feel is not enhanced.Further, since the distal ends of the first bristles 11 have difficultyin entering the interproximal areas and the periodontal areas, it isdifficult to enhance the cleaning performance. On the contrary, if thestep "d" is more than 4.0 mm, the second bristles 12 interfere with thedistal ends of the first bristles 11 to thereby make it impossible toprovide for a sufficient massaging effect. Moreover, since brushing ismade only by the first bristles 11 having a smaller grade of stiffness,cleansing performance cannot be enhanced.

In the case of this embodiment, since the bristles each having the firstbristles 11 and the second bristles 12 formed on opposite ends of thebristle folded into two parts are used for forming each tuft 1, manyfirst bristles 11 are located on one side of each tuft 1 and many secondbristles 12 are located on the other side. Also, in all of the tufts 1,fit angles α (see FIG. 2) of the flat line 22 are evenly arranged withrespect to a longitudinal axis L of the toothbrush.

A device and procedures for forming the bristles in tapered form andfinishing the side faces of the bristles to the above-mentioned surfaceroughness at one stage of manufacturing a toothbrush according to thisembodiment will now be briefly described. The toothbrush according tothis embodiment is manufactured from a toothbrush obtained by foldingbristle members each of which has column-like ends both having ball-likeportions at their foremost ends into two parts generally at the center,and embedding them respectively in the bored holes 21 with the use ofthe flat lines 22. Then, the bristles of this toothbrush are ground intoa tapered form by a wire brush. Subsequently, they are ground by a nylonbrush so that their side faces are caused to have the above-mentionedsurface roughness. In this process, one of the ball-like potions formedat their both ends distinguishes by grinding.

As shown in FIGS. 7 and 8, the abrasive device used for manufacturing atoothbrush according to this embodiment includes first abrasive means103 having a pair of cylindrical wire brushes 101, 102 which rotate indifferent directions, second and third abrasive means 104 and 105, andmoving means 107 for causing a distal end of the fiber material tocontact the rotating wire brushes 101 and 102, so that the toothbrush106 is gradually moved in the longitudinal direction of the wire brushes101, 102 while planarly rotating the toothbrush 106 on the wire brushes101, 102. Fourth abrasive means 122 having a pair of cylindrical nylonbrushes 120, 121, which rotate in different directions, is disposed at aforward location of the third abrasive means 105.

The first abrasive means 103 through the third abrasive means 105 eachhave a pair of cylindrical wire brushes 101, 102 as shown in FIG. 8. Thewire brushes 101, 102, in the form of one pair as one set, are rotatablymounted on a brush mounting base 108 and caused to rotate in differentdirections as indicated by arrows A and B of FIG. 8, by a brush rotationmotor 109.

That is, as shown in FIG. 8, the pair of wire brushes 101, 102 includesrotation transmitting gears 112, 113 engageable with a bevel gear 111disposed on a distal end of a drive shaft 110 of the brush rotatingmotor 109. The arrangement being such that rotation of the brushrotating motor 109 is transmitted to the wire brushes 101, 102 throughthe rotation transmitting gears 112, 113, so that the wire brushes 101,102 will rotate in different directions. Accordingly, the wire brush 101is rotated in the direction as indicated by an arrow A of FIG. 8, whilethe other wire brush 102 is rotated in the opposite direction asindicated by an arrow B of FIG. 8.

The wire brushes 101, 102 are swung generally in a perpendiculardirection (direction as indicated by an arrow C of FIG. 7) to thedirection of movement of the toothbrush 106 which moves in a way to drawa loop as indicated by an arrow W of FIG. 7. As shown in FIG. 9, thefirst abrasive means 103 through the third abrasive means 105 thusconstructed are arranged in predetermined position along the directionof movement of the toothbrush 106 in order as shown in FIG. 7, so thatthe contacting height between the bristles of the toothbrush 106 and thewire brushes 101, 102 is gradually increased.

That is, the wire brushes 101, 102 in the first abrasive means 103 arelocated in the position indicated by a solid line H₁ of FIG. 9, the wirebrushes 101, 102 in the second abrasive means 104 are located in theposition indicated by a one-dot chain line H₂, and the wire brushes 101,102 in the third abrasive means 105 are located in the positionindicated by a two-dot chain line H₃, such that the height of the wirebrushes 101, 102 are, either steppingly or steplessly, increased fromthe first abrasive means 103 to the second abrasive means 104 and thento the third abrasive means 105.

As shown in FIG. 7, the abrasive means 103 through 105 are arranged inthe direction of movement of the toothbrush 106 as follows. That is, thefirst abrasive means 103 is arranged at a rearward location of thesupplying toothbrush 106 before the toothbrush 106 is ground, the secondabrasive means 104 is arranged at a forward location of the firstabrasive means 103 at a predetermined space, and the third abrasivemeans 105 is arranged at a location which faces with the second abrasivemeans 104.

The fourth abrasive means 122 is provided to make a smooth grindingsurface because the grinding surface ground merely by the wire brushes101, 102, is not smooth enough.

The nylon brushes 120, 121 have abrasive grains kneaded to the surfaces.Since the fourth abrasive means 122 has the same construction as thefirst abrasive means 103 through the third abrasive means 105 exceptthat the brushes are nylon brushes, description of the common parts isomitted.

Next, the procedures for grinding the toothbrush 106 using the abovedevice will be described briefly. When the toothbrush 106, which is notyet ground into the tapered form as mentioned above, is supplied to thedevice, the toothbrush 106 is pinched at its head portion by atoothbrush holder, not shown, with the bristles facing downward. Thetoothbrush 106 is gradually and continuously moved, by the moving means107, in the direction as indicated by an arrow W of FIG. 7. At thattime, as shown in FIG. 8, the toothbrush 106 is rotated about the headportion in a horizontal plane. Then, as shown in FIG. 7, the toothbrush106 contacts the wire brushes 101, 102 of the first abrasive means 103rotating at a high speed but in opposite directions, and gradually movesin the longitudinal direction of the wire brushes 101, 102 whileplanarly rotating on the wire brushes 101, 102.

In this first abrasive means 103, the toothbrush 106 contacts the wirebrushes 101, 102 which are set to position as indicated by a solid lineH₁ of FIG. 9. That is, the foremost ends of the bristles of thetoothbrush 106 contact the wire brushes 101, 102. Then, the toothbrush106 is ground by the wire brushes 101, 102 which swing in a generallyperpendicular direction to the direction of movement of the toothbrush106 as indicated by the arrow C of FIG. 7, through interaction ofrotation and swinging of the wire brushes 101, 102.

During the time when the toothbrush 106 contacts the wire brushes 101,102, cold water is introduced in order to reduce a possible deformationof the bristles and wash out the grinding powders. The cold watercirculates after the grinding powers are recovered through a filter suchas non-woven fabric and paper. When the grinding is finished in thefirst abrasive means 103, the toothbrush 106 is ground by the secondabrasive means 104 next arranged as shown in FIG. 7. In this secondabrasive means 104, the toothbrush 106 contacts the wire brushes 101,102 which are set to the position indicated by the one-dot chain line H₂of FIG. 9. That is, the toothbrush 106 contacts the wire brushes 101,102 at its area extending slightly towards its base from its distal end.The toothbrush 106 is ground likewise by the wire brushes 101, 102through interaction of rotation and swinging of the wire brushes 101,102.

When the grinding is finished in the second abrasive means 104, thetoothbrush 106 is ground by the third abrasive means 105 next arrangedas shown in FIG. 7. In this third abrasive means 105, the toothbrush 106contacts the wire brushes 101, 102 which are set to the positionindicated by the two-dot chain line H₃ of FIG. 9. That is, thetoothbrush 106 contacts the wire brushes 101, 102 at its area extendingslightly towards its base from its distal end. And the toothbrush 106 isground likewise by the wire brushes 101, 102 through interaction ofrotation and swinging of the wire brushes 101, 102.

When the grinding is finished in the third abrasive means 105, thetoothbrush 106 is ground by the fourth abrasive means 122 next arrangedas shown in FIG. 7. In this fourth abrasive means 122, the toothbrush106 contacts the nylon brushes 120, 121 which are set to the sameposition where the wire brushes 101, 102 are set in the third grindingmeans 105, i.e., the position as indicated by the two-dot chain line H₃of FIG. 9. The toothbrush 106 is ground likewise by the nylon brushes120, 121 through interaction of rotation and swinging of the nylonbrushes 120, 121. The toothbrush 106, for which the grinding is finishedvia the above-mentioned four grinding processes, is then released fromits state held by the toothbrush holder in the moving means 107 andtransferred to an outlet port not shown.

According to the toothbrush of this embodiment thus constructed, thefirst bristles 11 each take a tapered form as indicated by the equation(I) in case the factorial coefficient n=0.29 to 0.51, and the distalends of the first bristles 11 project further than the second bristles12 with the step d formed on the distal end of each first bristle 11.Accordingly, the first bristles 11 are readily flexed only at the distalends, without decreasing the stiffness of individual bristles. Further,the first bristles 11 can contact the teeth and the gums earlier thanthe second bristles 12 so that a comfortable sense of feel can beprovided when brushing. Moreover, the distal ends of the first bristles11 readily enter into the interproximal areas and the periodontal areasto thereby efficiently remove dirt and dental plaque from the teeth. Inaddition, the distal ends of the first bristles 11 can easily massagethe gums near the interproximal areas and periodontal areas which weredifficult to be massaged in the conventional manner.

In case the factorial coefficient n is in the range of from 0.29 to0.51, the following items are all satisfied: (1) the first bristles 11are of a configuration which makes it easy to enter the interproximalareas and the periodontal areas, (2) the most appropriate stiffness forsatisfying both the effects of cleansing performance and massagingperformance is given; (3) the service life of the first bristles 11 isenhanced; and (4) the sense of feel is comfortable. Thus, the aboverange can be described as the best range for the factorial factor n.

Further, according to the toothbrush of this embodiment, the distal endsof the second bristles 12 are located in a lower position than thedistal ends of the first bristles 11. Accordingly, by co-acting with thefirst bristles 11 whose distal ends are readily flexed, there can beobtained, in addition to the above-mentioned effect, such an effect thatdirt and dental plaque on the surfaces of the teeth and gums can bescraped off by the distal end portions.

That is, the toothbrush according to this embodiment is comfortable insense of feel rendered to the teeth and gums during brushing. It isexcellent not only in cleansing performance of the surfaces of the teethand gums but also in cleansing performance of the interproximal areasand the periodontal areas. Moreover, the toothbrush of this embodimentis excellent in massaging effect of the gums including those parts inthe interproximal areas which would otherwise be difficult to bemassaged. The toothbrush according to this embodiment includes all ofthose effects.

The toothbrush according to the present invention is not limited to theabove embodiment. For example, the tufts 1 may be constituted by foldingtwo types of bristles into two parts, the first type of bristles havingthe first bristles 11 formed on opposite ends thereof, and the secondtype of bristles having the second bristles 12 formed on opposite endsthereof In the above embodiment, although the head portion 2 is of astepped form having the step D, the head portion 2 may have a flat uppersurface.

In the above embodiment, the first bristles 11 are located on one sideand the second bristles 12 are located on the other side with referenceto the flat line 22, using the plurality of bristles of FIG. 3. In thealternative, the first bristles 11 and the second bristles 12 may bemixedly located on the same side, using the bristles of FIG. 3. Otherparts of the toothbrush of this invention may also be modified accordingto necessity without departing from the gist of the invention.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

Industrial Applicability

The toothbrush according to the present invention is excellent withregard to the performance of cleansing the surfaces of teeth and gums,the areas between adjoining teeth, and the marginal areas between theteeth and the gums; and is excellent with regard to the performance ofmassaging the gums, is comfortable in sense of feel, and is satisfactoryin providing a long service life of the bristles.

We claim:
 1. A toothbrush comprising:a plurality of tufts each of which comprises a plurality of bristles embedded respectively in bored holes which are vertically and laterally formed in a head portion of the toothbrush; wherein:each of said tufts comprises first and second bristles, and in each of said tufts, a total of the first and second bristles is at least 50% of the bristles in each tuft; said first bristles are tapered bristles having a factorial coefficient n=0.29 to 0.51 in the following equation (I); distal ends of said second bristles are located in a lower position than distal ends of said first bristles; and vertical intervals between each of said bored holes are from 1.2 mm to 3.0 mm, and lateral intervals between each of said bored holes are from 0.75 mm to 1.5 mm;

    r(x)=a{(L-x)/L}.sup.n                                      (I)

where r(x): sectional radius x: length from base of each bristle L: length to distal end from base of each bristle a: sectional radius in case x=0[=r(0)] n: factorial coefficient.
 2. A toothbrush according to claim 1, wherein each of said tufts includes from 10% to 90% of said first bristles and from 90% to 10% of said second bristles.
 3. A toothbrush according to claim 1, wherein a step d between the distal end of each of said first bristles and the distal end of each of said second bristles is from 0.5 mm to 4.0 mm.
 4. A toothbrush according to claim 1, wherein an outer diameter of bases of each of said first bristles and each of said second bristles is from 0.15 mm to 0.30 mm, and an inside diameter of each of said bored holes is from 1.2 mm to 2.4 mm.
 5. A toothbrush according to claim 1, wherein said second bristles each have a ball-like portion formed on a distal end portion thereof.
 6. A toothbrush according to claim 5, wherein said second bristles are tapered towards the distal ends. 